A typical conventional machining simulation apparatus employs a single tool model to cut away part of a material model and check for interference of the tool model with the material model. In other words, this type of apparatus controls the relative positions of the tool model and the material model according to an axis movement command, whereby if the axis movement command is a cutting feed command, the region where the tool model and the material model overlap with each other is removed from the material model as a cutting region and if the axis movement command is a rapid traverse command, the region where the tool model and the material model overlap with each other is identified as an interfering region.
In particular, as shown in FIG. 5A, as a first step of its operation, such a conventional simulation apparatus causes a display unit 50 to show on its screen a machine model 51 representing a table on which a workpiece is mounted, a jig model 52 representing a jig that grips the workpiece, a material model 53 representing the workpiece to be machined, and a tool model 54 representing a tool used for machining. Secondly, in accordance with axis movement commands for cutting feed, the tool model 54 is moved relative to the machine model 51, the jig model 52, and the material model 53 so as to calculate the region where the tool model 54 and the material model 53 overlap with each other as a cutting region 55, remove the cutting region 55 from the material model 53, and then update the shape of the material model 53.
In this process, if a tool 540 having a diameter of d is used in the actual machining as shown in FIG. 6A, defining the tool model 54 as a cylinder whose cross section is circular having the same diameter as the tool 540 in this process will result in a cutting region 55 calculated as a cylinder having the same cross sectional area as that of the tool model 54. Alternatively, as shown in FIG. 6B, if the tool model 54 is defined approximately as a polygonal column whose cross section is a polygon inscribed in a cylinder of the same diameter as that of the tool 540, the cutting region 55 will be calculated as a polygonal column having the same cross sectional area as that of the tool model 54.
Subsequently, as shown in FIG. 5B, if the tool model 54 is retracted from the material model 53 according to an axis movement command for rapid traverse, the machining simulation apparatus checks for any interference of the tool model 54 with the material model 53, the jig model 52, and the machine model 51. In this processing, the model defined as having the shape of a cylinder or a polygonal column shown in FIG. 6 is used as the tool model 54 to check if there is any interference between the tool model and the updated version of the material model 53 from which the cutting region 55 of the shape of the cylinder or polygonal column has been removed.
According to this type of interference check, however, due to a computational error in removing the cutting region 55 from the material model 53, the machined portion in the updated material model 53 from which the cutting region 55 has been removed (i.e., the recess shown in FIG. 5B) may not completely match the tool model 54. In this case, the interference check may detect a minute interference between the tool model 54 and the material model 53, causing an alarm to be issued. Accordingly, one conventional approach is to define the region where the machined portion of the updated material model 53 and the tool model 54 overlap with one another as an interference region, calculate the volume of the interference region, and determine that no interference exists if the calculated value does not exceed a predetermined allowable value.
Japanese Patent No. 2,628,914 and Japanese Published Unexamined Patent Application No. 2000-284819 disclose machining simulation apparatuses with interference check capabilities.